Collapsible mold cores are generally known to the art, being typically used on molded plastic containers and the like which have undercuts in the core so that, without the core collapsing, the finished, molded piece could not be removed from the core.
Specifically, in Von Holdt U.S. Pat. No. 4,533,312, a recent design of a collapsible mold core for manufacturing straight-walled buckets and the like is shown. The collapsible mold core has members surrounding a tapered, central core member. Accordingly, as the members surrounding the central core member slide in longitudinal manner along the tapered, central core member, they also move inwardly to provide collapse of the core.
While the design of U.S. Pat. No. 4,533,312 exhibits many significant advantages, it and other designs have certain significant disadvantages that limit its use. For example, the outer core members are relatively thin and fragile, being moved between their molding and their collapsed positions by a control system which is operated from outside of the collapsible core. Because of this, when the mold sequence is for any reason out of step with itself, or a newly-molded object fails to be removed from the mold, and the mold thereafter closes, the collapsible core can be seriously damaged. For example, if the mold happens to close while the outer mold members are in their collapsed position, where they are longitudinally advanced beyond the central core member, the mold can be catastrophically destroyed.
Likewise, where side cores are used to form bucket handle attachment sites and the like, in the prior art the side cores may be operated hydraulically as a function of the molding machine, or mechanically by a cavity slide operated by the parting line opening and activating the cavity slide with an angle pin. Once again, in the event of a malfunction so that the molding steps take place out of their prescribed order and the side core is in the wrong position, severe damage can take place in the mold.
Likewise, in the prior art collapsible mold cores, when one molds a straight side container at a fast cycle, the walls of the container may show drag marks. These may be not acceptable, particularly when a smooth-sheen finish is being used for printing on the container.
Additionally, the outer mold core portions which move longitudinally relative to the central core member have been operated in the prior art by threaded side pins, which connect the outer core members to drive means outside of the core, to advance and retract the outer core members, moving them between their collapsed and molding positions. It has been found that the threaded pins sometimes break during operation of the collapsible core. The broken piece can then fall in between the respective mold halves, and cause catastrophic damage on the next closing of the mold.
The invention of this application provides a selfcontained mold having a collapsible core which provides solutions to the difficulties mentioned above, and others as well. The collapsible core of this invention eliminates many of the outside controls, to provide reliable opening and closing of the mold, with consequent collapse and reformation of the core as an automatic consequence of the mold opening and closing action. It becomes far less likely that an error by the operator, improper installation of the mold, or another mistake or failure will result in damage to the mold of this invention.